A method for calculating the mechanical specific energy of air hammer drilling

Air hammer drilling is currently an important technology for improving the drilling speed and efficiency in hard rocks. In order to evaluate the operating efficiency of air hammer drilling bit in real time and improve the controllability of drilling operation, this paper studied the method for calculating the mechanical specific energy of air hammer drilling. Based on previous theories related to mechanical specific energy, the mechanical structure and drilling mechanism of air hammer drilling bit were analyzed, and some parameters (e.g. impact efficiency and impact velocity) were introduced to correct and improve the mechanical specific energy calculating model. Then, the energy transfer efficiency (η_tr) was put forward to assist analyzing air hammer drilling efficiency. Finally, on the basis of foresaid theoretical model the software for calculating the mechanical specific energy of air hammer drilling was developed, which can scientifically evaluate the drilling efficiency of air hammer drilling bit by making comprehensive use of various continuous curve sections, such as drilling parameters, rock mechanical parameters, mechanical specific energy and energy transfer efficiency. In addition, it was verified based on the drilling data of Yuanba Block. It is indicated that the evaluation on the drilling efficiency from the aspects of air hammer’s mechanical specific energy and energy transfer efficiency which are obtained by means of the proposed calculation method is basically accordant with the actual situations on site. In addition, the method studied in this paper is of great significance to evaluate air hammer drilling efficiency, optimize drilling parameters and perform post-drilling analysis.